The present invention discloses a method and a system for an improved propeller drive of the underwater kind.
Certain kinds of propeller drives for boats are arranged on the hull bottom of the boat, as opposed to, for example, propeller drives which are arranged at the aft of the boat. In such propeller drives, the exhaust gases from the engine to which the drive is connected are usually let out via an exhaust channel, through an exhaust outlet opening which is below the water line, and which is also below the hull of the boat.
With a propeller drive which is arranged on the hull bottom of the boat, when the boat is moving, the exhaust gases will rise upwards to the surface of the water, and dissipate behind the boat or to the sides of the boat. However, if the boat is standing still with the engine running, i.e. if the transmission of the propeller drive is in the idle position, the exhaust gases will still rise upwards, but at least part of the exhaust gases may hit the hull bottom of the boat. Although usually imperceptible by those aboard the boat, there is still a desire to reduce or entirely eliminate any noise, vibrations and other undesired effects caused by this effect.
Thus, as stated above, there is a need for a solution by means of which an underwater propeller drive arranged on the hull bottom of a boat can be made even quieter and offer an increased degree of comfort when the engine is running and the transmission of the propeller drive is in the idle position.
According to an aspect of the present invention, a method is provided for controlling the exit of exhaust gases from an engine which is used to power an underwater propeller drive which is arranged at the hull bottom of a boat. The method of an aspect of the invention comprises letting the exhaust gases flow from the engine through an exhaust channel and exit through a first underwater exhaust outlet in the underwater propeller drive.
According to the method of an aspect of the invention, if the engine is running and the transmission of the propeller drive is in neutral position, a second underwater exhaust outlet is opened for letting exhaust gases in the exhaust channel exit in a position closer to the hull bottom of the boat than the first underwater exhaust outlet.
As will be discussed in more detail below, tests have shown the inventors of the present invention that this solution, i.e. the use of a second underwater exhaust, considerably reduces or even eliminates any noise, vibrations and other undesirable effects caused by the exhaust gases when the engine is running and the transmission is in the idle position, if the second exhaust outlet is closer to the hull bottom of the boat than the first exhaust outlet is.
The second underwater exhaust outlet can be designed or obtained in a number of ways within the scope of the present invention. In one embodiment of the invention, the second underwater exhaust outlet is a vent in an underwater housing of the propeller drive, and is arranged closer to the hull bottom of the boat than the first underwater exhaust outlet is.
In another embodiment of the method of the invention, a first part of the underwater propeller drive is rotatable about a second part which is attached to the hull bottom of the boat, and the exhaust channel comprises a first opening in the first part which faces a second opening in the second part. The first and second openings have corresponding forms and shapes, so that they cooperate to form part of the exhaust channel. According to this embodiment of the method of the invention, the second underwater exhaust outlet is opened by means of rotating the first part to a predefined angle relative to the second part. Thus, in this embodiment, the second underwater exhaust outlet is suitably opened by means of non-coinciding portions of the first and second openings.
The present invention also discloses a system which operates according to the basic principles described above.
Both the method and the system of the invention will be described in more detail in the text which follows below,